Prediction of the need for postoperative mechanical ventilation in myasthenia gravis: thymectomy compared to other surgical procedures.

In a recent report Leventhal, Orkin, and Hirsh described a scoring system felt to be of value in predicting the need for postoperative mechanical ventilation in patients with myasthenia gravis undergoing thymectomy. Leventhal, et al. identified four risk factors felt to have predictive value, namely: (1) duration of myasthenia gravis greater than or equal to 6 years, (2) chronic respiratory disease, (3) dose of pyridostigmine greater than or equal to 750 mg per day, and (4) vital capacity less than or equal to 2.9 litres. Forty-six patients with myasthenia gravis who received 68 general anaesthetics were studied retrospectively. They represented the past 10 years' anaesthetic experience with myasthenia gravis at the Vancouver General Hospital. The patients were divided into two groups: (1) those who underwent thymectomy, and (2) those who underwent procedures other than thymectomy. Using the risk factors of Leventhal, et al., a predictive score was assessed for each patient; the time of postoperative tracheal extubation was also noted for each patient. From this study it was concluded that the scoring system proposed by Leventhal, et al. may have been of some value in predicting whether or not a particular patient undergoing thymectomy was likely to need ventilation postoperatively. In 41 myasthenics who had procedures other than thymectomy, however, this scoring system was found to be of no value.